Thermal treatment and separation process



May 29, 1956 R. c. OLBERG ET AL 2,748,061

THERMAL TREATMENT AND SEPARATION PROCESS Fild Aug. 18, 1951 2 Sheets-Sheet l l I I I I i I A Mo|eular DisHHcrHon n B Once Through Mild Thermal 'Trea+men+ C, Two S+age Ther'rhM i Trea+men+ kesudue \OOO l! .J 3 600 0 1d O E .I J 1 I 1 1 l I o so /ow1- REDUCE-D CRUDE.

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Ralph C. O\berg Charla? Brewer By: ed-a/ k heir Aqerd" May 29, 1956 R. c. OLBERG ET AL THERMAL TREATMENT AND SEPARATION PROCESS 2 Sheets-Sheet 2 Filed Aug. 18, 1951 :0 AND", 3935 UZIOW mv m r\ mw ow .6 96 mm Q? 1| om 3%] v-QQPW Stan l ma AN/ I I M Q 3 02 U dU UCL/J EUQU OF.

lnvenforzs-- Ralph C. Olber'g a 5 By: &u

United States PatenrO THERMAL TREATMENT AND SEPARATION PROCESS Ralph C. Olberg, Walnut Creek, and Charles P. Brewer,

El Cerrito, Califl, assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application August 18, 1951, Serial No. 242,524

4 Claims. (Cl. 196-50) This invention relates to an improved process for the thermal treatment of hydrocarbonoils, and pertains more particularly to a proce s adapted for the production of distillates, the larger proportions preferably being of the character of kerosene and gas oils from heavy oil, such as crude petroleum, reduced crude oil or the like.

Various methods have been proposed and utilized for the recovery of various materials, such as gasoline, kerosene, light gas oil, heavy gas oil and lubricating oil distillates, from petroleum oils, both for their direct use and for use as feed stocks to various conversion processes. Thus, the gas oil distillates, both light and heavy, constitute an important feed stock for both thermal and catalytic conversions in the production of gasoline therefrom. Socalled topped crudes and short residues, as well as certain heavy crudes oftentimes are subjected to a thermal treatment known as visbreaking to efl ect a viscosity reduction, followed by separation of vaporizable components, both natural and formed in the visbreaking, as one or more distillate fractions. The separation may be effected in one or more stages, for example by a partial separation at atmospheric or higher pressure followed by a second separation at subatmospheric partial pressure, as by steam stripping, or by a single separation at a subatmospheric pressure, as by vacuum flashing.

Since the distillates boiling higher than gasoline are converted by catalytic cracking to gasoline of higher octane number than by thermal cracking, it is a general practice, where catalytic cracking capacity is available, to attempt to produce from the heavier petroleum oil materials a maximum proportion of distillate product to be utilized as catalytic cracking feed stock. In the case of mixed-base or asphaltic base crudes, this is generally done by a topping operation followed by the well-known vacuum flashing operation. Another practice is to heat and distil from the heavier oils and residual oils as much vaporizable material as possible while converting the ultimate residue to coke. However, the coke thus produced is generally of poor quality and of little market value. Still another practice is to subject the heavier oils to a deasphalting operation. The deasphalting process is effective only with certain types of crude stocks, and the cost is high.

In all such cases, the primary objective is to obtain from the crude oil, and particularly from the topped or reduced crude, a maximum amount of distillate oil with an optimum distribution of products or fractions thereof and an optimum residue product of suitable quality (utility) all consistent with the most economical and profitable operations of a particular refinery. In general, this means ice that it is highly desirable to secure from a given heavy petroleum oil the maximum amount of distillate material of the general character of kerosene and gas oil distillates while at the same time producing an amount of a residue of suitable quality which is blendable to a minimum amount of suitable fuel oil.

' It is therefore a principal object of the present invention to provide an improved process for the production from a heavy petroleum oil of a maximum amount of distillate oil having a composition distribution which is optimum in a feed stock for catalytic cracking operations in the production of motor fuels. 7

.Another object of the invention is to provide an improved process for the thermal conversion of heavy petroleum stocks, such as reduced crude, to increase the yield of distillate oils therefrom.

A further object is to provide a process for the thermal conversion ofheavy components of petroleum oils containing thermally unstable and cokable components into distillate oils of high catalytic cracking quality while avoiding the formation of coke, and producing a residue prodnot which is blendable to a suitable fuel oil, e. g., a specification SSF at 122 F. residual fuel oil.

It is a further object to provide a process for increasing the yield of distillate oils of the boiling range of kerosene and light gas oil from heavy oil stocks while minimizing the formation of gas and lighter distillate material from higher boiling materials of the stock and at the same time producing a minimum amount of residue product which is readily blendable to a suitable fuel oil.

The foregoing objects will be better understood and others will become apparent from the description of the invention which will be made with reference to the accompanying drawing wherein:

Fig. I is a graphical representation of the molecular weight distribution of a product obtained from a representative reduced crude before and after a mild thermal treatment, and after a thermal treatment according to the present invention; and

Fig. II is a diagrammatic flow sheet showing a preferred method of practicing the invention wherein a reduced crude-or so-called straight run residue (long residue) is subjected to a thermal treatment and separation operation to recover therefrom a maximum amount of gas oileffectively converted largely to distillate oils in a continuous manner, without causing undesirable conversions to occur, by subjecting the heavy oil stock to a first mild thermal conversion and separation operation followed by a second thermal conversion treatment of the residual oil separated from the first separation operation and separation of the distillable components of theresulting mixture from a final residue which is blendable to a substantially coke-freestable. fuel 'oil; The first mild thermal conversion'treatment is carried out under conditions of temperattire and residence time to elfect a partial conversion of heavier components of the stockto lighter components of the gas oil boiling range and the first separation step is carried out to effect the separation of at least the major proportion of the light gas oil components of the mixture, and lighter components, as distillate materialfrom there maining residual oil. The second thermal conversion treatment is carried out under conditions of temperature, pressure and residence time, which ensure conversion of a substantial portion of the remaining heavier components of the residual oil to components of the gas oil range while at the same time maintaining the mixture essentially in the liquid phase, whereby cokable components of the mixture are maintained diluted with liquefied distillable components, thus minimizing conversion of cokable components to coke. The second separation step is effected under conditions to ensure the removal of essentially all of the distillable components and a simultaneous reduction ofthe temperature of the remainingresidue so that thermal'conversion thereof to coke is negligible and the residue. is separated as-a product which'is readily blendable to a suitable fuel oil.

The first stage of the foregoing generally described two-stage process is operated under conditions which effect only'aminor amount of thermal conversion but at the same time an effective recovery of distillable components from the oil stock. Accordingly, the heating of'the oil mustbecoordinated with the separation operation. Since the usual feed stocks, such as reduced crude and the like, contain gas oil components with boiling points below the temperature (about 425 C.) at which thermal conversion of heavy components becomes significant at reasonable residence times, heating of the oil as a stream in a coil or tube at substantially atmospheric or slightly superatmospheric pressure produces a considerable vapor phase with resultant relatively low residence time, which is de. sirable; Such heating under substantially atmospheric pressure accordingly requires that the first stage separation be effected under substantially atmospheric pressure or under subatmospheric pressure. The first stage separation is usually carried out without the addition of any further amount of heat to the material, consequently, the temperature of the oil remaining in the separation zone becomes lower because of the removal of heat of vaporization of material distilled therefrom. Separation under reduced pressure (vacuum) results in more complete removal of distillable material; however, it is preferable to effect an incomplete removal of distillable material in this stage so as to provide a diluent effect of some heavy oil components and non-coking conditions in the subsequent heating step. The first stage thermal treatment is carried out at a temperature of from about 425 to about 475 C. and with a corresponding residence time in the heating zone of from about 6 to about 0.5 minutes. A preferred temperature range isfrom about 440- toabout 460 C., with corresponding residence times of from about to about 1 minute;-the pressure is preferably-of the order of from about atmospheric to about pounds-per square inch gauge. In the case of the usual topped: or

reduced crude, for example of a typical California mixedbase crude, from about 45% to about 65%, and preferably from to is suitably removed as overhead material in the first stageof the process.

The second stage of the two-stage process is-operated under conditions which effectsubstantial thermal con version of the residual product from the first stage into gas oil components and effective recovery of the thusformed gas oil components as distillate from the remaining residue product. The overhead recovery will depend. on the nature of the crude aswell as the extent to which it has been reduced. For the reduced crude indicated, there is obtainable a total recovery of overhead material corresponding to from about to about 88% of the original heavy oil, the overhead preferably being atleastv about of the initial heavy oil. In order to carry out the second stage heating under conditions to provide a maximum of distillable products while avoiding cokeformation, it is required to subject the residual oil from the first stage to somewhat more severe conversion conditionsthan in the first stage while at the same time maintaining the system in a state which minimizes reactions which produce coke. Accordingly, the material is heated in the second stage toa temperature of from about 440 C. to about 470 C., preferably from about 450 C. to about 460 C., for a period of time of from about 5 to about 10 minutes, while maintaining the system under a substantially superatmospheric pressure (100-300 p. s. i. g.) sufficient to maintain it essentially as a liquid phase system. By maintaining the system essentially liquid phase, reactions which lead directly to coke formation are minimized. In order to lower the temperature below conversion level essentially simultaneously with removal of distillable products, the stream of products is quickly separated in a separation zone of considerably reduced pressure, for example atmospheric pressure and preferably subatmospheric pressure, such as l0l00 mm. Hg. absolute pressure, preferably at 10-50 mm. Hg. absolute pressure, with rapid cooling of the residue product due to rapid removal of heat ofvaporization 0f distillable material in the overhead stream.

It is contemplated'according to the invention to'pass a portion or all of the overhead product stream from the second stage separation into the first-stage separation zone for any stripping action therein which it can provide as well as a means for condensing and removing therefrom heavier components which it is desired to subject to further mild thermal conversion, particularly when the second stage separation is essentially a flash separation with only a small amount of fractionation. It is also contemplated to recover a heavier fraction of the gas oil from the distillable products separated in the second stage separation and to blend it with the residual 'oil duce-Inild thermal cracking can be practiced in such a weights as determined by a molecular distillation.

from the first stage and to subject said heavier gas oil to further thermal conversion treatment in the second stage heating zone while utilizing it as diluent for cokable components of the residual'oil to minimize coke formation from cokable components of the residual oil;

The process of the present invention is based on several facts'which havebeen established by experimental studies. Such studies have shown that operations on reduced crude in regions -of temperature and contact time which promanner'as to'yield sizable increases in distillate products and at the same time maintaining residue quality for the production of stable, homogeneous residual fuel oil. The general-applicability of the process of the invention to stocks representing various geographical locations and Continent and Texas stocks,and Kuwait reduced crude.

The constitution, on a molecular weight basis, for example, of a l7.4 API reduced mixed Los Angeles Basin crude'is'indicated'by the solid line (A), in Fig. I, which shows the distribution of components by molecular It is to be seen that this reduced crude contains about 55% of material of 500 molecular weight or lower. By a mild and controlled thermal treatment and separation process products'are obtained from the same reduced crude such that the molecular weight distribution of the total composite thereof-is representable by the intermediate line (B) in Fig. I. Thus, distillate products'of 500 molecular weight or lower are obtained to the extent of as much as 80.-% of the-reduced crude; about 65% of the material has a molecular weight of about 400 or lower. However, by a two stage process in accordance-with the present invention, products are obtained from the same reduced crude as represented by the lowermost line (C); It is to be seen that essentially-the same amount of distillable material is recoverable in this case having a molecular Furthermore, unlike conventional theram s 1 amounts of gas and gasoline (about 5-6% wt.), the chief product being gas oil.

As already discussed, increased residence time and/or higher temperature result in greater thermal conversion of the heavy oil material being treated, under a given set of other conditions. The tendency of coke formation during heating of residual materials is also dependent on the. relative concentration of the cokable materials (high molecular weight components containing a high proportion of aromatic carbon atoms). It is readily understood, therefore, that the rate of flow of the heavy oil stock through the heating coil is adjusted in accordance with the particular temperatures maintained therein.

It is to be seen that a particular advantage of the process of this invention is the suppression of condensation reactions which lead eventually to coke formation, while at the same time effecting the desired thermal degradation of the heavier oil components to lighter gas oil components, and all the time minimizing thermal degradation of desirable gas oil components, both initially present and formed in the process, to less desirable substances such as gaseous and low boiling hydrocarbons.

Having discussed various factors involved in the process of this invention and various features thereof, a more detailed description thereof will be made with reference to Fig. II.

In accordance with the essential features of the process, a suitable heavy oil stock, such as a reduced crude or straight run residue, is suitably preheated, (not shown) as by heat exchange against hot overhead product streams in the process, and then delivered as by line 11 and pump 12 to a suitable heater, such as a coil or tube heater represented by 14, wherein it is heated as a single stream or as a plurality of streams to a suitable temperature effective for producing a minor amount of thermal conversion of heavier oil components of the reduced crude, for example about 425 to 475 0., preferably about 440 to 460 C., under a pressure of from about atmospheric to about 45 p. s. i. g., and at a residence time of about 2 to 5 minutes. All or the larger portion of the thermally treated stream(s) of material can be fed into the lower section of a suitable fractionator and separator 15, a minor portion being delivered as desired by line 16 to the upper part of the separator to ensure the presence of liquid phase on the inner wall surfaces of the separator to minimize coke formation thereon. Alternatively, all or a major portion of the heated stock can be fed into the top of the separator or at an intermediate point. The separator is suitably provided with a small number of members adapted to ensure intimate liquid and vapor phase contacting therein while maintaining relatively free flowing conditions for the fluids therein. The construction details and operation will depend on the desired degree of fractionation therein. The separation of remaining residual material and distillable material in separator 15 is effected at a pressure ranging from only slightly below the pressure on the oil stream in the heater to a pressure of about 10 to 20 pounds per square inch lower, although still lower pressures, even vacuum, can be utilized. The vaporized material is removed overhead through line 17, and, if desired, is dephlegmated in dephlegmator 19, with the condensate being returned by line 20 to the separator and the uncondensed overhead stream being withdrawn through line 21. The extent of dephlegmation effected in 19 is relatively small, in general being merely sufficient to prevent entrainment and physical carryover of liquid heavier components. As indicated already, the separation in fractionator 15 is carried out so as to effect a removal of about 50 to 60% of the material in the overhead stream in line 21.

The remainder of the oil stock is withdrawn from the bottom of the separator by means of line 22, pumped by pump 24 to a suitably higher pressure, for example about 200 p. s. i. g., transferred by line 25 to the heating coil(s) of a suitable heater 26 (or in a suitable separate coil in heater 14), wherein the stream of residual oil is heated in essentially liquid phase sufficient to effect thermal conversion of a substantial portion of the remaining heavy oil components to distillable gas oil components. A temperature of about 450 to 460 C. is effectively employed with a residence time of about 5 to'lO minutes.

The thus thermally treated residual oil is then fractionated and separated in fractionator 29, preferably under subatmospheric pressure, for example at a pressure of about 1050 mm. Hg, absolute, into an overhead product stream and a bottoms residue product stream. Fractionator 29 is suitably provided with elements for intimately contacting liquid and vaporous materials, such as perforated plates, disc and doughnut-type trays, bubble trays, and the like, as will be readily understood in the art, the amount of fractionation required being relatively small. The separation is also suitably carried out essentially as a flash separation with only sufiicient fractionation and/or dephlegmation to prevent entrainment and carryover of residue components.

The overhead product stream from fractionator 29 is removed by line 30 and preferably partially dephlegmated in dephlegmator 31, with return of the separated liquid phase by line 32 to the fractionator, while the net 0verhead stream is joined by line 34 to the overhead product from the first fractionator in line 21.

A portion or all of the overhead stream in line 30, or

of the dephlegmated stream in line 34, is advantageously delivered to a lower section of the fractionator 15, as by line 35, wherein it serves as additional stripping medium and at the same time heavier components of the overhead from fractionator 29 are condensed and returned to heater 26 for further mild thermal treatment thereof. Another advantageous feature of the invention is that heavier condensate material can be withdrawn from an upper trap-out tray, for example by either or both of lines 36 and 37, and recycled to line 22 and the heater 26, wherein it is subjected to further mild thermal treatment thereof while it in turn serves as diluent for cokable components of the residue portion of the residual oil, thereby assisting in minimizing coke production from such components. The residue remaining in the bottom of fractionator 29 is withdrawn at a temperature of about 380 to 400 C., by means of line 39, provided with pump 40 and heat exchanger 41. Since this residue is relatively hard material when cooled to ambient atmospheric temperature and is advantageously blended with suitable blending stock, commonly known as cutter stock, (e. g. catalytic gas oil, gas oil extract, etc., usually substantially aromatic, i. e., 50%+ aromatics) while the residue is still at an elevated temperature, the'blending is effectively carried out by blending the cutter stock directly, as by line 38, with the hot residue in line 39. In some cases a portion or all of the blending can be effected by recirculating a portion of the residue through line 42 to a baffled section of the bottom of the separator 29, as indicated, and feeding the cutter stock into the recirculating residue stream, as indicated by line 44, with withdrawal of blended fuel oil through line 45.

The combined overhead product from the first and second stage separations can be utilized directly as feed stock for catalytic cracking operations, as indicated by line 46, or it is suitably fractionated in a fractionating column 47, into a gas fraction (light hydrocarbons), removed in line 48, a thermal gasoline fraction removed in line 49, and a gas oil product removed in line 50. It will be understood that the total product above gasoline (dew point about 200 C.) can be utilized as feed stock for catalytic cracking operations, or it can be fractionated into two or more fractions and the fractions utilized as desired. The total gas oil product may comprise both light gas oil and heavy gas oil components, with the light gas oil usually predominating; however, the process is advantageously carried out under conditions, to effect a.

7 substantial conversion of heavy gas oil components to light gas oil components, particularly in the second stage of the process.

The practice of the invention and the advantages thereof will be more fully understood from a comparison of operating conditions used and properties of resultant products obtained (1) when applying the process to a mixed Los Angeles Basin reduced crude and (2) when processing the same reduced crude (a) in a single stage thermal conversion and separating operation to yield the same proportion of overhead product and (b) in a two stage thermal conversion and separating process wherein both the first and second stages are carried out at substantially atmospheric pressure. The comparative operating conditions and results are given in Table I.

TABLE I Thermal treatment and separation of reduced crude Two-Stage One- Pmcess 1st Stage stage 2nd Stage Conditions:

Temp, C 43 1 470 1 430 460 480 446 Press, Atm, abs 2 0.49 2 0.57 2 0.56 13.6 13. 6 2 0. 50 Liquid Phase Res.

Time, Min 4.6 7.2 36.2 5 2 5.2 30.0 Products, percent w. Re-

duced Crude:

Gas 0.7 1. 9 2.3 2.0 2. 2.1 Gasoline, 205 (l... 2. 2 4. 0 4. 4.1 6. 0 4.1 Gas Oil, 205 G 55. 5 74.5 72. 7 68. 3 70. 0 74.4 Residue 41. 6 l9. 6 20. 5 3 25. 6 3 22. 0 19. 4 Catalytic Cracking Products from Gas Oil, percent \v.:

25. 3 24. 5 24. 5 24.8 25.4 25. 9 26. 6 26. 9 26. 0 24. 2 37. 0 37. 0 37.0 37.0 37. 0 lie. 11.8 11.9 11.6 12. 2 13.4 Residue Quality as Measured by Precipitation Index 4 a. 40-45 74 74 55. 6 (i3. 5 72 1 Temperature of liquid phase during both treatment and separation.

2 Partial pressure of oil about 0.5 atrn. with 0.5 atm. nitrogen.

3 Distillate separated with fractionation at overhead vapor temperature of 330 C. at 10 mm. Hg pressure and pot temperature of about 380 0.; residue of same quality and less than is readily obtainable at higher separation temperature but still below thermal conversion temperature, e. g., 400-410 O.

4 Precipitation index is indicative of the least soluble component in the residue. It is the percentage of a-methyl naphthalene in a a-metl1yl naphthalene-octane mixture which just fails to dissolve the least soluble ornponent of the residue. Lower values indicate better quality.

It is to be seen from the comparative data given in Table I that by the two-stage process of the present invention distillate catalytic cracking feed stock can be obtained from a reduced crude in essentially the same proportions as by a one-stage process or by a two-stage process in which both stages are carried out at substantially atmospheric pressure, with essentially the same quality of the distillate as catalytic cracking feed stock as that obtained from the two-stage atmospheric pressure process and superior in quality to that obtained by a one-stage process when quality is measured by coke-make in a standardized catalytic cracking process, while at the same time the residue resulting from the two-stage process of this invention has a substantially lower precipitation index than the residues obtained by the comparative processes, the precipitation index being a measure of the degradation of the residue components of the reduced crude during the processing regardless of the presence or absence of distillable heavy gas oil components in the residue and being a measure of the blendability of the residue to suitable fuel oil.

We claim as our invention:

1. The method of thermally treating and separating a reduced mixed-base crude containing not over about by weight of distillable components having a molecular weight up to about 500, the remainder being higher molecular weight distillable components and at least a substantial portion of non-distillable residue components,

'to produce and recover therefrom oil distillate having improved catalytic cracking characteristics and a residue product enriched in non-distillable components in reduced amount which is readily blendable to a stable fuel oil, which method comprises: (1) subjecting the reduced crude to a mild thermal treatment at a temperature of from about 425 C. to about 475 C. under substantially atmospheric pressure and for a correlated time of from about 0.5 to about 6 minutes to produce light gas oil components from heavy oil components and separating gas, gasoline and light gas oil components from a remaining residual product containing a substantial proportion of non-distillable residue components, in admixture with a heavy gas oil product recovered as hereinafter described, (2) subjecting the remaining residual product under substantially super-atmospheric pressure of 300 p. s. i. g. and while maintained essentially in the liquid phase to a more severe thermal treatment at a temperature of from about 440 C. to about 470 C. to convert further heavy oil components to light gas oil components while minimizing degradation by condensation of heavy oil components, (3) subjecting the thus-treated admixture of residual product and heavy gas oil to a separation operation under substantially subatmospheric pressure below about 100 mm. of Hg pressure and recovering further light gas oil components, a heavy gas oil fraction, and a remaining residue product of a high molecular weight, essentially non-distillable components which is blendable with a suitable blending oil to a stable fuel oil, and recycling the recovered heavy gas oil fraction for utility in step 2.

2. The method of thermally treating and separating a reduced mixed-base crude containing not over about 60% by weight of distillable components having a molecular weight up to about 500, the remainder being higher molecular weight distillable components and at least a substantial portion of non-distillable residue components, to produce and recover therefrom substantially over 60% by weight of oil distillate of components having a molecular weight of about 400 and lower and having improved catalytic cracking characteristics and a residue product enriched in non-distillable components in reduced amount which is blendable to a stable fuel oil, which method comprises: l) subjecting the reduced crude to a mild thermal treatment at a temperature of about 440460 C. and

- for a correlated time of from about 0.5 to about 6 minutes and subjecting the thus-treated reduced crude to separation with the recovery of gas, gasoline and light gas oil components having molecular weights below about 400 from a remaining residual product containing non-distillable residue components and distillable heavy oil components, (2) subjecting the separated remaining residual product under substantially superatmospheric pressure of 100-300 p. s. i. g. and while maintained essentially in liquid phase to a more severe thermal treatment at a temperature of 440470 C. for a time of about 5-10 minutes to convert heavy oil components to light gas oil components while minimizing degradation by condensation of heavy oil components, and (3) subjecting the thustreated residual product to a separation operation under substantially subatmospheric pressure below about 100 mm. of Hg and recovering a gas oil distillate comprising a further substantial proportion of light gas oil components having molecular weights below about 400 and heavy gas oil components and a remaining residue product of high molecular weight, essentially non-distillable components which is blendable with a suitable blending oil to a stable fuel oil.

3. The method in accordance with claim 2, wherein the gas oil distillate recovered in step (3) is recycled to the separation operation in step 1) wherein the light gas oil components having molecular weight below about 400 are separated as part of the light gas oil components and the heavy gas oil components are separated with the remaining residual product.

4. The method in accordance with claim 2, wherein the gas oil distillate recovered in step (3) is separated into its light gas oil components and its heavy gas oil components, the thus separated light gas oil is combined with the vaporized products from the separation operation in step (1) to give a total separated product of molecular weight up to about 400 of about 80-85%, based on the reduced crude, and the separated heavy gas oil components are recycled to admix with the residual product from step (1) and heated therewith in step (2).

References Cited in the file of this patent UNITED STATES PATENTS Heid Nov. 30, 1937 Watson Oct. 4, 1938 Nofsinger Jan. 2, 1940 Atwell Apr. 29, 1941 Roberts Jan. 27, 1942 Morrell Apr. 28, 1942 Dunham Apr. 24, 1945 Houdry May 16. 1950 

1. THE METHOD OF THERMALLY TREATING AND SEPARATING A REDUCED MIXED-BASE CRUDE CONTAINING NOT OVER ABOUT 60% BY WEIGHT OF DISTILLATE COMPONENTS HAVING A MOLECULAR WEIGHT UP TO ABOUT 500, THE REMAINDER BEING HIGHER MOLECULAR WEIGHT DISTILLATE COMPONENTS AND AT LEAST A SUBSTANTIAL PORTION OF NON-DISTILLABLE RESIDUE COMPONENTS, TO PRODUCE AND RECOVER THEREFROM OIL DISTILLATE HAVING IMPROVED CATALYTIC CRACKING CHARACTERISTICS AND A RESIDUE PRODUCT ENRICHED IN NON-DISTILLABLE COMPONENTS IN REDUCED AMOUNT WHICH IS READILY BLENDABLE TO A STABLE FUEL OIL, WHICH METHOD COMPRISES: (1) SUBJECTING THE REDUCED CRUDE TO A MILD THERMAL TREATMENT AT A TEMPERATURE OF FROM ABOUT 425* C. TO ABOUT 475* C. UNDER SUBSTANTIALLY ATMOSPHERIC PRESSURE AND FOR A CORRELATED TIME OF FROM ABOUT 0.5 TO ABOUT 6 MINUTES TO PRODUCE LIGHT GAS OIL COMPONENTS FROM HEAVY OIL COMPONENTS AND SEPARATING GAS, GASOLINE AND LIGHT GAS OIL COMPONENTS FROM A REMAINING RESIDUAL PRODUCT CONTAINING A SUBSTANTIAL PROPORTION OF NON-DISTILLABLE RESIDUE COMPONENTS, IN ADMIXTURE WITH A HEAVY GAS OIL PRODUCT RECOVERED AS HEREINAFTER DESCRIBED, (2) SUBJECTING THE REMAINING RESIDUAL PRODUCT UNDER SUBSTANTIALLY SUPER-ATMOSPHERIC PRESSURE OF 100-300 P. S. I. G. AND WHILE MAINTAINED ESSENTIALLY IN THE LIQUID PHASE TO A MORE SEVERE THERMAL TREATMENT AT A TEMPERATURE OF FROM ABOUT 440* C. TO ABOUT 470* C. TO CONVERT FURTHER HEAVY OIL COMPONENTS TO LIGHT GAS OIL COMPONENTS WHILE MINIMIZING DEGRADATION BY CONDENSATION OF HEAVY OIL COMPONENTS, (3) SUBJECTING THE THUS-TREATED ADMIXTURE OF RESIDUAL PRODUCT AND HEAVY GAS OIL TO A SEPARATION OPERATION UNDER SUBSTANTIALLY SUBATMOSPHERIC PRESSURE BELOW ABOUT 100 MM. OF HG PRESSURE AND RECOVERING FURTHER LIGHT GAS OIL COMPONENTS, A HEAVY GAS OIL FRACTION, AND A REMAINING RESIDUE PRODUCT OF A HIGH MOLECULAR WEIGHT, ESSENTIALLY NON-DISTILLABLE COMPONENTS WHICH IS BLENDABLE WITH A SUITABLE BLENDING OIL TO A STABLE FUEL OIL, AND RECYCLING THE RECOVERED HEAVY GAS OIL FRACTION FOR UTILITY IN STEP
 2. 